books.google.co.uk - World War I saw the submarine develop into a potent weapon of war. The German submarine campaign almost defeated Britain during the spring of 1917. By striking at the shipping that supplied her, it has been estimated that Britain came within six weeks of starvation....https://books.google.co.uk/books/about/U_Boats_Destroyed.html?id=E_TE_ARPXdMC&utm_source=gb-gplus-shareU-Boats Destroyed